Purification of aromatic acids using zinc, aluminum, or magnesium



United States Patent 3,150,181 PTJRKFECATION OF ARGMATIC AClDS USlNGZTNC, ALUMKNUM, OER MAGNESIUM John 3. Erodbeclr and John B. Wilkes,Albany, Calih, assignors to Qalifornia Research Corporation, SanFrancisco, (Ialih, a corporation of Delawm'e No Drawing. Filed Jan. 4,1962, Ser. No. 164,374 11 (Jlaims. (Cl. Mil-58) This invention relatesto a novel method of improving the quality of dibasic aromatic acids.More particularly, this invention relates to a novel method of removingcolor bodies from said acids.

Aromatic dibasic acids are being increasingly used for preparing finequality synthetic fibers as well as other polymeric materials. Thedemand for the dibasic acids has led to a variety of methods ofsynthesis of these acids. When the aromatic group is benzene, many ofthe routes use the analogous xylene as the precursor.

Among the methods of oxidizing the alkyl groups of the dialkylarenes isthe use of aqueous sulfur type reagents. See, for example, W. G. Toland,I. Am. Chem. Soc., 82, 1911 (1960). It has been found that the dibasicacids obtained by this method contain color forming impurities whichmake the acids unacceptable for a variety of applications, particularly,fine grade fibers. Even when the acid appears colorless, the productsobtained therefrom may become discolored during formation or processing.

It has now been found that discoloring contaminants, which the presentin the acid obtained by use of an aqueous sulfur type oxidant, where theoxidation is carried out in the presence of ammonia or ammonium ion, maybe removed by treatment with zinc, magnesium, or aluminium metal. Theimpurities are thought to include some sulfur-containing compounds, butthis invention is not intended to be limited to sulfur compounds, sincethe exact nature of the impurities is unknown.

The material treated with the. metal is the crude amide, rather than theacid. When using an aqueous sulfur-type oxidant in the presence ofammonia, the oxidate will usually contain as its major organicconstituents diamide, monoamide and ammonium salts. The term crude amideis intended to define this product mixture.

The purification merely requires heating the crude amide with a smallamount of zinc, magnesium or aluminium is the essential absence of air.A preferred method is to follow this treatment with a further treatmentwith a heavy metal salt. Activated carbon may be used in this inventioneither before, after or during the treatment with the metals and isfound to enhance the purification.

After the treatment with the metals and metal cations, the metals may beremoved and the solution hydrolyzed to the desired dibasic acid. Whileit is not known why these metals aid in the removal of color formingbodies, it would appear that the aluminum, magnesium and zinc act in areductive manner.

The purification is operable for any dibasic acid obtained by oxidationof an aromatic hydrocarbon by an aoueous sulfur-type oxidant in thepresence of ammonia, i.e., sulfur, sulfate, thiosulfate, bisulfite, etc.As examples of acid amides by amides it is intended to include monoanddiamides and ammonium saltsthe precursors to the bibasic acids, whichare operable are the following: 1,4-napthadioic amide, 1,6-napthadioicamide, biphenyl- 4,4-dicarboxylic amide, terephthalic amide, isophthalicamide, etc. While polynuclear aromatic dibasic acids may be used in thisprocess, the mononuclear aromatic dibasic acids are preferred, i.e.,phthalic, isophthalic and terepht'nalic, with particular preference forthe latter two acids.

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The zinc, magnesium and aluminum may be in any form. It is preferredthat the metals be finely divided or powdered, for in this state themetal is most efficiently used. The amount of metal used may varywidely, amounts as little as 0.1 weight percent of potential acid valuesgiving a demonstrable improvement. (By potential acid values is intendedthe total weight of materials which would give acid on hydrolysis. Thisincludes amides, ammonium salts and the acid itself.) The amount ofmetal will usually depend on the degree to which the crude amide iscontaminated and the desired qumity of the product. While any amount ofthe metals may be used, amounts ordinarily will not exceed 20 Weightpercent of the potential acid values. Usually amounts in the range of 1to 5 weight percent will be satisfactory. When very large amounts areemployed, much of the metal remains unreacted, but with a great exces, amore rapid reaction is obtained.

Many of the common heavy metal soluble salts may be employed. Thepreferred metal cations are mercury, lead, cadmium and antimony. Theamount of the salt is not critical and will usually be within the rangeof 0.1 to 10 Weight percent of the potential acid values. The preferredrange is 0.5 to 5 weight percent. Mixtures of the salts may be used. Theanion may be any of the common anions such as the halides: chloride andbromide; acetate, sulfate, etc., as long as a Water-soluble salt isobtained.

The temperature of the treatment with the metals as well as the metalcations will usually be at least 70 F. No advantage is obtained byincreasing the temperature above 500 F. and temperatures in the range250 F. have been found most practical from an operating standpoint andare preferred. The reaction time for the treatment with the metals Willdepend on their physical form, the rate of reaction increasing withincreasing surface area. The metals in the powdered form are thereforepreferred. The metals treatment will usually not be extended beyond afew hours and will generally be limited to less than two hours, times inthe range of 1 minute to 1 hour having been found satisfactory.

Prolonged treatment with the heavy metal cations is also not required. Afew minutes have been found practical and the time may vary from 1minute to a few hours. The time period is one of expedience and is notcritical.

While not essential to the purification, the use of activated carbondoes enhance the final result. Any of the adsorbent forms of carbon maybe used, e.g., activated charcoal. The carbon may be introduced prior orsubsequent to the metals treatment and may be present during the metalstreatment. Practical amounts of carbon have been found in the range 0.1to 5 weight percent of the potential acid values.

The essential absence of oxygen is required during the treatment withmetals. It has been found that if the crude amide is treated in thepresence of air, little, if any, improvement occurs. While initially thecolor of the crude amide solution may diminish, the color rapidlyreturns. When only the metal treatment is used, oxygen must be excludeduntil the hydrolysis step. However, once the solution is carried throughthe treatment with the heavy metal salt, the presence of oxygen has nosignificant effect on the quality of the resulting dibasic acid.Nevertheless, for best results, it is preferred to continue to maintainthe solution in an inert atmosphere, e.g., nitrogen, argon, hydrogen,etc., until the hydrolysis step.

The metal cations may be removed in a variety of Ways, i.e., ionexchange resins, chelating agents, etc., the most practicable beingprecipitation with H 8 and then filtration. If hydrogen sulfide is usedfor removal, it is preferable to remove all of the hydrogen sulfide,prior to I5 hydrolysis of the amide. This may be conveniently done bystripping with, for example, steam, nitrogen, etc. Prior to the H 8treatment, any excess metal may be removed by filtration.

The purification may be carried out batchwise or in a continuous manner.

The quality of the isophthalic acid has been correlated With the percenttransmission of light through aqueous solutions of the sodium salts inthe ultraviolet and visible range. Either the percent transmission maybe determined at particular wave lengths, e.g., 3400 A., or the percenttransmission may be determined as the average of a narrow range of wavelengths by the use of filters. The latter may be reported as Tristimuluscolors using a Lumetron Model 402E colorimeter. These methods helppredict the quality of polymers obtained from the acid.

The following examples will serve to further illustrate the inventionand are not intended as limitations.

Example I Crude isophthalic amide (300 g.) (A) was stirred with 2.4 g.carbon at 200 F. for 30 minutes. Throughout the metals and carbontreatment, the temperature was maintained at about 200 F. and thesolutions were kept in an inert atmosphere of nitrogen. The solution wasfiltered and the filtrate slurried with 12 g. zinc and then stirred for30 minutes.

The solution was then filtered removing the excess metal and 12 g. ofmercuric chloride added, the mixture stirred for 5 minutes, and thenfiltered.

The metal cations were then precipitated out with hydrogen sulfide andthe solution filtered. Excess hydrogen sulfide was removed by bubblingnitrogen through the hot solution. After the removal of the hydrogensulfide,

sulfuric acid was added to obtain a pH 2 and the solution heated at 420F. for one hour to hydrolyze the amide. The solid which separated wasfiltered and washed at 100 F., slurried in 240 m1. of sodium bisulfatesolution at 420 F. and heated for one hour to ensure completehydrolysis. The acid was then filtered, washed and dried at 200 F.

The isophthalic acid obtained had a UV percent transmission: at 4000 A.of 95.5; at 3400 A. of 65.0.

When 0.6 g. of lead acetate was used in place of the mercuric chlorideusing the above procedure, the isophthalic acid had a UV percenttransmission: at 4000 A. of 88.0; at 3400 A. of 21.5.

When 0.6 g. of cadmium sulfate was used in place of mercuric chlorideusing the above procedure, the isophthalic acid had a UV percenttransmission: at 4000 A. of 88.0; at 3400 A. of 14.0.

When no metals were used, using the same procedure, the isophthalic acidobtained had a UV percent transmission: at 4000 A. of 83.4; at 3400 A.of 0.0.

When 0.6 g. of antimony trichloride was used in place of mercuricchloride with isophthalic amide (B) using the above procedure, theisophthalic acid had a UV percent transmission: at 4000 A. of 85.3; at3400 A. of 30.0

When the same procedure was carried out without the use of zinc andantimony with isophthalic amide (B), the isophthalic acid had a UVpercent transmission: at 4000 A. or" 79.5; at 3400 A. of 0.0.

Example ll and the solutions were kept in an inert atmosphere ofnitrogen. The solution was filtered hot and 6 g. of

mercuric chloride added and allowed to react for 5 min- '11he lettersindicate the various batches of isophthalic amic e.

All UV determinationswere made in 0.5 M phthalic Sll1 tion of 3 N sodiumhydroxide in a 5 cm. cell.

' for 60 minutes.

4. utes and then hydrogen sulfide introduced to precipitate the metals.

The hydrogen sulfide was stripped 01? with nitrogen and 2.4 g. of carbonadded, and the mixture stirred for 30 minutes. The solution was filteredand then subjected to hydrolysis as described in Example I.

The isophthalic acid had a UV percent transmission: at 4000 A. of 93.2;at 3400 A. of 44.0.

Example III Crude isophthalic amide (300 g.) (C) was stirred with 2.4 g.carbon for 30 minutes. The temperature was maintained at 200 F.throughout the treatment with carbon and aluminum and the isophthalicamide was kept in an inert atmosphere of nitrogen. The solution wasfiltered and 0.6 g. of aluminum added and the mixture stirred Activatedcarbon (2.4 g.) was added and the mixture stirred for an additional 30minutes, then filtered and subjected to the hydrolysis described inExample I.

The isophthalic acid had a UV percent transmission: at 4000 A. of 91.2;at 3400 A. of 15.0.

Isophthalic amide (C) treated without the aluminum according to.theprocedure of Example IH had a UV percent transmission: at 4000 A. of83.3; at 3400 A. of 0.0.

- Example IV Crude isophthalic amide (300 g.) (D) and activated carbonwere mixed and stirred for 30 minutes. The

7 temperature was maintained at 200 F. and the solutions were kept in anatmosphere of nitrogen throughout the treatment with magnesium andcarbon. The carbon was filtered oti and 0.6 g. of magnesium added, andthe mixture stirred for 30 minutes. Activated carbon was then added andthe mixture stirred for 30 minutes and filtered. The filtrate was thensubjected to the hydrolysis treatment described in Example I.

The resulting acid had a Tristimulus percent transmission: blue, 87.5;green, 95.0; amber, 95.6. Acid obtained without magnesium treatment hadTristimulus percent transmission-z blue, 82.2; green, 92.9; amber, 93.4.

Using the same procedure as Example IV with crude isophthalic amide (E)and 0.3 g. of zinc instead of magnesium, and also excluding the secondcarbon treatment, gave isophthalic acid having Tristimulus percent 4transmission: blue, 88.4; green, 94.9; amber, 95.2. Without the zinctreatment the acid had Tristirnulus percent transmission: blue, 82.7;green, 91.4; amber 91.6.

As will be evident to those skilled in the art, various modifications ofthis process can be made or followed, in the light of the foregoingdisclosure and discussion, with out departing from the spirit or scopeof the disclosure or from the scope of the following claims.

We claim:

1. In a process which comprises the preparation of mononuclear aromaticdibasic acids free of color-forming contaminants from mononucleardialkyl arenes by contacting said arenes with an aqueous sulfur-typeoxidant in the presence of ammonia to form a crude amide reac tionproduct, the improvement which comprises contacting said crude amidewith from 0.1 to 10 weight percent of the potential acid values of saidcrude amide with a member of the group consisting of zinc, aluminum andmagnesium, at a temperature in excess of 70 F. and in the essentialabsence of oxygen.

2. A method according to claim 1 wherein the treatment with metals isfollowed with contacting the crude amide product with from 0.1 to 10weight percent of the potential acid values of a member of the groupconsisting of mercury, lead, cadmium and antimony cations.

3. A method according to claim 1 wherein contact with activated carbonis included as an additional step.

4. A method according to claim 2 wherein contact with activated carbonis included as an additional step.

5. A method according to claim 2 wherein the metal is zinc and the metalcation is mercury, and the treatment is carried out at a temgerature inthe range of about 160-250 F.

6. In a process which comprises the preparation of isophthalic acid freeof color-forming contaminants from meta-Xylene by contacting saidmeta-Xylene with an aqueous sulfur-tyhe oxidant selected from the groupconsisting of sulfur, sulfate, thiosulfate and hisulfite in the presenceof ammonia to form a crude amide reaction product, the improvement whichcomprises contacting said crude amide With from 0.1 to 5 Weight percentof the potential acid values of said crude amide with zinc at atemperature in excess of 70 F. in the essential absence of oxygen andthen contacting the reaction product with mercuric cation.

7. A method according to claim 6 wherein aluminum is used in place ofzinc.

8. A method according to claim 6 wherein magnesium is used in place ofZinc.

9. A method according to claim 6 wherein the antimony cation is used inplace of mercuric cation.

10. A method according to claim 6 wherein lead cation is used in placeof mercuric cation.

11. A method according to claim 6 wherein cadmium cation is used inplace of mercuric cation.

References Cited in the file of this patent UNITED STATES PATENTS2,734,079 Aroyan et a1 Feb. 7, 1956 2,789,999 Iezl Apr. 23, 19573,058,997 Taylor et a1 Oct. 16, 1962 OTHER REFERENCES Toland, Jour. Am.Chem. Soc. vol. 82, p. 1911-1916 (1960).

1. IN A PROCESS WHICH COMPRISES THE PREPARATION OF MONONUCLEAR AROMATICDIBASIC ACIDS FREE OF COLOR-FORMING CONTAMINANTS FROM MONONUCLEARDIALKYL ARENES BY CONTACTING SAID ARENES WITH AN AQUEOUS SULFUR-TYPEOXIDANT IN THE PRESENCE OF AMMONIA TO FORM A CRUDE AMIDE REACTIONPRODUCT, THE IMPROVEMENT WHICH COMPRISES CONTACTING SAID CRUDE AMIDEWITH FROM 0.1 TO 10 WEIGHT PERCENT OF THE POTENTIAL ACID VALUES OF SAIDCRUDE AMIDE WITH A MEMBER OF THE GROUP CONSISTING OF ZINC, ALUMINUM ANDMAGNESIUM, AT A TEMPERATURE IN EXCESS OF 70*F. AND IN THE ESSENTIALABSENCE OF OXYGEN.